Pretty much every plant in my group of 20 has a single curled blade on its leaf (or 1 or 2 more). It kind of twists. So whats going on?

I'm thinking it may be because my ph lvl is around 7-8 and is too high. I'm working on lowering that. Has anyone seen this before?

I'm hoping someone can shed some light for me. Thanks in advance for the help.